Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

2.6. SUMMARY
2.6 Summary
• CO 2 storage and enhanced oil recovery has been ongoing at Weyburn since 2000. A downhole
geophone array was installed in 2003 to monitor microseismicity in one pattern.
• The array has detected microseismicity, and events have been located by ESG using automated
location algorithms.
• I have manually sorted the events between those that can be reliably identified as microseismic
events, those that are due to operator activities (perf-shots, drilling, etc.), and have discarded
those that where a clear P- and S-wave succession cannot be identified.
• 86 microseismic events have been located over 5 years of monitoring. This represents a low rate
of microseismicity relative to many producing carbonate fields.
• Events during Phase IB can be divided into in 2 clusters, near the production wells to the NW
and SE. Rates of seismicity can be correlated with activities in these wells.
• Although depth errors are large, events do appear to be located in the overburden. Without
geomechanical modelling it is not clear whether this represents fluid migration from the reservoir,
or merely failure induced by stress transfer into the overburden.
• The low rates of microseismicity, combined with only one array, means that it has not been
possible to image the triaxial stress state in the reservoir, nor to track pressure or fluid migration
fronts.
25